Question: If $a + 5b = 6$ and $5x + 4y = -6$, what is $3a + 40y + 50x + 15b$ ?
Answer: $= 3a + 15b + 50x + 40y$ $= (3) \cdot (a + 5b) + (10) \cdot (5x + 4y)$ $= (3) \cdot (6) + (10) \cdot (-6)$ $= 18 - 60$ $= -42$